Current limiting reactor



Aug. 2, 1966 A. B. TRENCH CURRENT LIMITING REACTOR Fil ed May 24, 1953 4Sheets-Sheet 1 Aug. 2, 1966 I A. B. TRENCH 3,264,590

CURRENT LIMITING REACTOR Filed May 24, 1963 4 Sheets-Sheet 2 Aug. 2,1966 A. B. TRENCH CURRENT LIMITING REACTOR 4 Sheets-Sheet 5 Filed May24, 1963 Aug. 2, 1966 A. B. TRENCH CURRENT LIMITING REACTOR 4 Sheets-Sh4 Filed y 24, 1965 FIG. 53%? 20a 0'0 06 0'0 Ooob 00 0000 00 0000 0Qooo'o o'o 000000 000000 900000 000000 QQ po 21'0 2u 2/2 F IG] 7 UnitedStates Patent 3,264,590 CURRENT LIMITING REACTOR Anthony Barciay Trench,Downsview, Ontario, Canada, assignor to Trench Electric Limited,Toronto, Ontario, Canada, a corporation of Canada Fiied May 24, 1%3,Ser. No. 282,937 Claims priority, application Great Britain, May 29,1962, 26,614/62 11 Claims. (Cl. 336-60) The present invention relates toelectrical inductive devices having a plurality of coaxially disposedcoils electrically connected in parallel. Each coil consists of a singleconductor having a single turn per axial pitch.

The coil construction is applicable to coils, transformers, wave traps,reactors or the like. The description herein will however be limited tocurrent limiting reactors and wave traps in electrical powertransmission systems.

it is common practice in prior electrical devices to provide plural,parallel, current-sharing wires, rather than a single wire, toconstitute a single conductor. By providing plural wires, objectionablelosses and heating effects due to eddy currents and PR losses areminimized. Also, the extremely large diameter necessary for singlestrand Wires is not mechanically feasible.

In the inductor art, current sharing between the various plural,parallel conductors has generally been accomplished by a technique knownas transposition. In transposition of windings, the individual strandsor conductors must be maintained at the same average diameter to insureequal current distribution between the various conductors. Otherwise,the AC. impedance of one strand is considerably less than that of theothers and most of the current will flow through this strand, causingexcessive heating thereof and possible overload, leading to reactormalfuction. This is accomplished by changing the diameter of eachwinding as it assumes a different axial position, thus necessitatingsubstantially right angle bends in the strands in both the radial andaxial directions. Right angle bends, however, are undesirable becausethey are time consuming to fabricate and result in very bulky mechanicalconfigurations for substantial currents. Because of the radiallyextending wires necessary in transposed conductors and their mechanicalinterference with the axial turns, a great number of transposedconductors cannot be utilized in prior art reactors. Consequently, largecurrent capacity inductors require a small number of relatively largediameter wires. However, large diameter wires are undesirable because ofthe substantial power losses therein and the diiiiculty in handlingattendant therewith.

Fabrication of reactors having transposed windings requires themechanically complex operation of simultaneously winding and transposingall of the conductors about a common axis. The process of transposingconstitutes the formation of a rotation, or intertwining, of theconductors about one another so as to produce the desired effectiveelectrical equality between them. It clearly follows that all of theconductors must be handled simultaneously to achieve these transpositionconfigurations throughout the winding. This process is difiicult toperform and demands much manual labor on the part of skilled operators.

It is thus seen that prior art inductors employing transposed conductorsare diflicult to design mechanically and electrically because of theirinvolved geometric config uration and are not easily manufactured.

In addition, conductor diameter is generally the last parameterdetermined in the design of inductors with transposed conductors. Inconsequence, conductors of non-standard size, which must be especiallymanufac- Patented August 2, 1966 tured at great cost are usuallyemployed in order to achieve the necessary balanced currentdistribution.

It is an object of the present invention to provide a coil and method ofmanufacturing coils in which the prior requirement for transposing ofparallel conductors is completely eliminated.

It is another object of the present invention to provide a reactor coilthat is designed with a minimum of mechanical and electrical effort.

It is a further object of the present invention to provide a currentlimiting reactor capable of large current capacity and having aplurality of parallel conductors wherein the current in each conductoris relatively small compared with total reactor current to therebyminimize eddy current and PR power losses.

It is a further object of the present invention to provide a new andimproved current limiting reactor wherein standard cables are utilizablefor the conductors in virtually all desired configurations and whereinthe various conductors are connected in parallel between a pair ofreactor terminals and the induced in each of the plural coils issubstantially equal so excessive current is not drawn by any of thecoils.

It is an additional object of the present invention to provide a currentlimiting reactor wherein a plurality of parallel solenoidal coils areemployed for the reactive element and the across all coils is maintainedsubstantially equal by merely designing the number of turns in the coilsto the proper value.

It is still a further object of the present invention to provide a newand improved reactor coil which occupies minimum space and is not bulkyor difficult to manipulate in manufacture.

Yet another object is to provide a new and improved reactor which iseasily fabricated and lends itself to automatic construction techniquesand methods.

The present invention contemplates the solution of these and otherobjects by utilizing a plurality of helical coaxially disposed coils,said coaxial coils being connected in parallel and having relativelengths and cross sectional areas such that the induced across each coilis substantially equal. Thereby, the current through one coil does notbecome excessive and the unit is not subject to The coils connected inparallel are wound concentrically about a common axis so there is asingle burn-out.

turn per axial pitch.

According to the present invention, the solenoidal coils are wound tosatisfy the simultaneous equations governed by the formula:

where I r:=1,2,3..-P; s=1,2,3...p;

M =the specific mutual reactance between the rth and sth coil in whichspecific means the mutual reactance that would exist if each coilconsisted of only one v By this equation, the mutual and self-inductanceof each coil may be easily computed by hand or computer techniques sincethe geometric configuration of each coil is extremely regular. Whenutilizing this design formula,

it is possible to preselect the particular cross sectional area of eachconductor, the number of coils employed, and the current in each coilmaintaining the sum of all of the currents equal to the rated totalcurrent of the reactor unit.) After these quantities are preselected, itis then necessary only to determine the winding pitch and diameter ofeach coil. Since conductor size is predetermined, it should be apparentthat standard size conductors may be utilized in the present invention,thus obviating an im' portant contribution to the cost of prior artreactors.

For many designs of the reactor, it is necessary for the different coilsto .be terminated at different points around the periphery of the commonaxis. To connect the coils together in parallel relationship and to theexternal circuit, a connector having a plurality of spider armsextending radially from the common coil axis is provided at each end ofthe coil structure. The end of the coil is connectedto the arm to whichit is closest by conductors extending parallel with the axis of thecoil.

The coils are windable either on themselves or spaced from each other asdetermined by the presence or absence of insulation therein. The spacingof adjacent coils may be radial, axial, or both. It is generallypreferable, however, for the various coils to be radially spaced fromeach other to permit maximum cooling. Otherwise, temperature rise aslarge currents are supplied to the reactor becomes excessive.

In one embodiment of the invention, the entire apparatus is securedtogether by the oppositely located spider arms and an insulated rod orplurality of insulated rods extending between the spiders. In thisembodiment, the windings of the coils are located about an insulatedsleeve having a plurality of ventilating holes which permit circulationthrough the inductor structure of air or a suitable insulating, coolantgas or liquid. In other embodiment of the present invention, the coilsare secured in place by a pluraliy of insulating binding posts,extending between the two spiders about the interior periphery of thecoil construction.

With the present invention, it is not necessary for the conductors to beof the same dimensions, nor it is necessary for them to carry the samecurrent densities. In fact, it is frequently not desirable for all ofthem to have identical current densities because interior conductorspossess an inherent tendency to increase in temperature to a greaterextent than those at the exterior, due to their more confinedheat-dissipating environment. Accordingly, it is desirable for theinteriorly located conductors to carry smaller current densities thanthe outer conductors to enable them to generate power losses consistentwith their thermal capacities. In the present invention, the conductorcurrents may be preselected so as to best suit their thermal capacitiesin each particular location, which results in an appreciable saving ofconductor material, otherwise unobtainable with transposed windings.With the present invention, the conductor currents may be selected inthis manner while maintaining the induced in the parallel coilssubstantially equal.

Accordingly, it is yet another object of the'present invention toprovide a new and improved current limiting reactor wherein cooling ofthe reactor coils is promoted since the various parallel connected coilsare not of the same cross sectional area but have cross sections suchthat the outer coils carry greater current than the inner coils whilestill maintaining the induced in the coils substantially equal.

Because the coils are substantially cylindrical in shape, eachcomprising a single layer helix, and because there are no interferingtranspositions of conductors required between them, they may be wound athigh speed in a continuous operation. This operation is carried out bywinding the convolutions of the coils one after another. Since thisprocedure is not possible with transposed windings where all of theconductors must be simultaneously and intricately intertwined duringfabrication, the manufacturing process of the present invention ishighly advantageous in that it lends itself to facile and complete orsemi-automatic reactor unit fabrication.

The invention is illustrated by way of example in the accompanyingdrawings, wherein:

FIGURE 1 is a perspective view of a current limiting reactor constructedin accordance with the present invention;

FIGURE 2 is a side elevational view of the reactor of FIGURE 1;

FIGURE 3 is a top plan view of the reactor of FIG- URE 1;

FIGURE 4 is a fragmentary sectional view taken through the lines 44 ofFIGURE 3;

FIGURE 5 is a side view of the clamping structure illustrated in FIGURE4 wherein the clamp is shown as being taken along the lines 55;

FIGURE 6 is a fragmentary sectional view of the parallel spacedconductors taken along the lines 66 of FIGURE 4;

FIGURE 7 is an illustration of the insulating feet as secured to thereactor spider arms;

FIGURE 8 is a plan view of another embodiment of the present invention;

FIGURE 9 is a side fragmentary sectional view of the embodiment ofFIGURE 8;

FIGURE 10 is a sectional view taken along lines 1010 of FIGURE 9; and

FIGURE 11 is a partial sectional view of a wave trap.

Referring now to the drawings, shown in FIGURE 1 is a current limitingreactor. The air core reactor consists of a central apertured sleeve 21,electrically conductive spiders 23 and 24 at opposite ends thereof, anda plurality of concentrically disposed coils 25-30 (see also FIGS. 3 and4). Cylindrical sleeve 21 includes a plurality of substantially circularapertures 22 in the walls thereof. Apertures 22 permit the flow of airor some insulating coolant, such as freon gas, to circulate throughoutthe reactor to maintain the temperature thereof at a reasonable level.

Spiders 23 and 24 include a plurality of radially extending members (inthe illustrated embodiments, eight in number), for effecting connectionsbetween the ends of the coils. These coils are usually of differentlengths and hence terminate at various peripheral locations. The coils,25 to 30, inclusive are concentric about a common axis along whichinsulating rod 32 extends. Rod 32 compresses spiders 23 and 24 towardeach other to provide mechanical stability for the entire structure.Arms 33 and 34 of spiders 23 and 24, respectively, extend radially to agreater extent from rod 32 than the other arms of spiders 23 and 24 toestablish connections between the reactor and the electrical circuitryof a distribution system. In this manner, all of the reactor except theextending portions of arms 33 and 34 may be completely enclosed in asealed casing to permit circulation of a coolant around the coils. Coils25-30 are concentrically wound about a common axis whereat is locatedrod 32 and are radially separated from each other by a plurality ofinsulating spacers 35.

As :best seen in FIGURES 2, 3 and 4, each of the coils 2530 is a singlestrand coil and there in only one turn of conductor per axial pitch.Thus, as illustrated in FIGURES 3 and 4, coil 25 includes but a singlestrand or conductor extending in a direction about the axis of rod 32and at a substantially constant radial distance therefrom. Thisarrangement is maintained throughout a complete pitch of each windingand may be referred to as a helical winding. As best illustrated inFIGURE 4, the conductor in coil 25 does not extend parallel to spiders23 and 24' but is inclined with respect thereto by an amountcommensurate with winding pitch.

The windings 25-30 are coated with a suitable insulating material, suchas varnish, enamel or the like so they may be wound on each other.However, it is usually desirable to space the individual coils 25-30from each other by insulating spacers 35 to promote cooling the interiorportions of each coil. Insulating spacers 35 are spaced from about thecircumference of sleeve 21 between coils 25-30 to coincide with theposition of the radially extending arms of spiders 23 and 24 which arein alignment. As best illustrated in FIGURE 6 there are a plurality ofsuch elongated spacers 35 extending between each of the various coils25-30. The insulating spacers 35 extend between the spiders 23 and 24and maintain the radial position of each of the windings 25-30substantially constant and provide space for air or coolant circulationtherebetween. Radial spacing between the various coils 25-30 of thereactor is achieved by proper selection of the number of spacers. Thewidth or number of the insulating spacers is varied to accommodatedifferent radial spacings between adjacent coils.

As noted particularly from FIGURE 4 and from the respective drawings ofFIGURE 1, each of the coils 25-30, which are of the barrel or solenoidaltype has a different length in order to achieve the necessary balancedrelationship necessary in coils connected in parallel.

As illustrated in FIGURE 2, the winding of innermost coil 25 terminatesat a different peripheral point than the winding of its adjacent coil 26which also terminates at a still different point than that of itsoutwardly adjacent Winding 27. In order to connect these windings andall of the other coils of the reactor in parallel, conductors 42, 43 and44 extend in the same direction as the axis of the coils between theterminations of coils 25, 26 and 27, respectively (the otherterminations not being illustrated) and the radially extending arms ofspiders 23. Similarly, conductors 45, 46 and 47 connect the other end ofcoils 25, 26 and 27, respectively, to appropriate arms of the oppositespider 24. It is important that conductors 42 to 47 extend substantiallyparallel to the common axis of all of the coils 25-30 so they will haveminimum effect on the induced in each coil. By maintaining theconnecting conductors 42-47 substantially parallel to appropriate armsof the axis of coils 25-30, i.e., substantially perpendicular to thewindings of the coils (no induced in the various connecting conductorsresults to adversely affect the voltage across the reactor terminals.

The conductors are connected to the spiders by the clamping structure 48illustrated in FIGURE 5. Each clamp 48 mounted on the arms of spiders 23and 24 serves the dual purpose of maintaining spacers 35 in place and ofeffecting electrical connections between the coils and the arms of therespectively one of spiders 23 and 24. Each clamp is secured to itsrespective spider arm by a pair of nut-bolt assemblies 49 and 51 (seeFIGS. 1 and 5).. Clamp 48 comprises a pair of insulating bars 52 and 53substantially rectangular in cross-section. The insulators 52 and 53 aredisposed on opposite sides of the spider arm to 'which it is secured andhave projections 54 and 55 along one edge thereof abutting the spiderarm. The projections 54 and 55, located at one edge ofinsulators 52 and53, respectively, engage opposite sidewalls of the spider arms withwhich it is associated. Claws 56 and 57, located on the other edge ofinsulators 52 and 53, respectively, engage suitable slots in each ofinsulating spacers 35, extending from the arm of one spider to an arm ofthe other spider and terminal winding, terminal 46, which is theterminal end of a coil.

Recesses 65, 65a are provided at the end of insulating members 52 and 53in proximity to claws 56 and 57, respectively, so that the insulatingspacer 3'5 and winding terminal 46 fit in the grooves formed between theinsulators 52 and 53 and the spider arm. Insulating members 52 and 53,as well as the spider, are provided with bores 66 through which a bolt64 extends for securing the insulators to the spider arm.

The arms of spiders 23 and 24 are provided with grooves 67 and 68 forreceiving set screws 69 to maintain insulating feet 71 in place, asillustrated in FIG- URES 4 and 7. A threaded bore 72 is provided in oneside of foot 71 perpendicular to the wide face of spider arm 24, asillustrated in FIGURE 7, for securing the set screw 69 therein, wherebythe screw extends into the groove 68. When employing the reactorstructure in a vertical positon as illustrated, it is necessary toemploy grooves only in the lower spider arms. However, grooves areprovided in both spider arms 23 and 24, respectively, on the top andbottom of the reactor for uniformity of spider fabrication and for thepossibility of supporting the reactor in other positions. When thereactor is positioned so its axis is in the horizontal plane, supportinginsulators 71 are positioned perpendicular to the common axis of coils25-30 rather than parallel thereto as illustrated. In such anarrangement, it is necessary to employ the grooves of both spiders 23and 24 for securing the support insulators 71 therein. The number ofsupporting insulators 71 necessary is dependent upon their relative sizeto the total reactor structure. The radially extending grooves 67 and 68on the spider arms are provided for variably positioning the feet 71 tomaintain mechanical balance for the reactor.

When designing the reactor of the present invention, the windings ineach coil must be arranged to satisfy the simultaneuos equationsgoverned by the formula:

where p=the number of coils in the reactor; r=1,2,3 p;

s=l,2,3 p;

(rand s may or may not be equal) n and n the number of turns in coils rand s, respectively;

M =equals the specific mutual reactance between the rth and the sthcoil, in which specific means the mutual .reactance that would exist ifeach coil consists of only one effective turn, but is otherwisephysically unchanged;

i current designed to flow through coils r which is preselected; and

E=the designed voltage drop across the reactor with the coil parametersselected so that the current distribution between the various coils iscompatible with the heat dissipation capabilities of the coils.

Since each coil is connected in parallel, E is, of course, the samethroughout the design equations. In the reactor design, initially, aneducated guess as to the number of conductors and the size thereof ismade. The conductor is preferably designed to be of standard size andlow current rating to minimize losses. This is desirable because it doesnot necessitate manufacture of special conductors for fabrication of thereactor windings. Conductor size, of course, determines maximum currentin a particular coil which governs maximum temperature increase of thereactor from no load to full load.

Of course, the diameter of each coil must be greater than the interiorcoil to which it is adjacent by an amount greater than the adjacentconductor diameter plus insulation. It is preferable, moreover, todesign coil diameter slightly greater than this minimum quantity topermit coolant circulation. Axial winding pitch obviously cannot besmaller than the width of the conductor plus insulation thicknessthereon which comprises the particular coil. The axial pitch can exceedthis minimum value depending upon the number of turns of conductor inthe coil and the overall length of such coil thus obviating thenecessity for insulated conductors when the coils are spaced apart bothradially and axially to an extent suflicient to prevent electricalleakage therebetween.

After determining the size of each conductor, which ascertains itscurrent, each coil diameter and each winding pitch, the number ofwindings in each coil is computed from the equation by solving formutual and self reactance. This may be accomplished by manual orautomatic computation methods.

For many applications, it is desirable for the currents flowing throughinterior coils 25, 26 and 27 to be less than that flowing throughexterior coils 28 and 29 because of the ability to cool the greaterexposed surface area exterior coils more readily than the interior ones.The criteria in designing the number of coils and the current througheach coil is that the sum of the current through all of the parallelconnected coils be equal to the designed maximum current of the reactorunit and that the temperature rise be Within the designed limits.

If it is desired to provide a 300 volt reactor having a 600 ampererating at 60 cycles and an 80 C. temperature rise from no load to fullload, continuous operation, a reactor is fabricated having sevenconcentric coaxial cylindrical coils connected in parallel. The fourmost interior coils are wound from a A" x 7 conductor while the threemost exteriorly located coils are wound with a A x A" conductor. Withthis size conductors, the four inner coils carry 80 amps each, while theouter three coils carry 93 /3 amps each.

The winding pitch of the four interiorly located coils is that is, incoil 25 the distance between the upper edge 61 of winding 73 (FIGURE 4),is separated from the upper edge 74 of winding 75, of the next adjacentturn of conductor in the winding of the same coil, by a distance ofwhere points 61 and 73 lie in a plane parallel to the common axis ofcoils 2530. The four outer coils have a winding pitch of V 1. It shouldbe noted that in the example above, the winding pitch is greater forboth the inner four and outer three conductors than the conductor in theaxial direction of the coils. Since coil windings are wound on eachother, this is merely indicative of the layer of insulation on thestrands. Consequently, the Winding pitch in many cases is determinedwhen conductor size is designed.

In the design described supra, coil diameter and number of coil turnsare specifically designated in the table below:

As pointed out supra, the frictional number of turns is achieved byextending connecting wires to the spider arms, such wires being parallelto the axis of the coils.

It is generally desirable when manufacturing the reactor as will appearfrom the next example to be described to wind the coils on each other inan axial direction because of the ease with which this may beaccomplished compared to the difficulty in providing axial spacingbetween single turn layers. Accordingly, winding pitch is generallydetermined by selection of conductor size and is not usually a variablein determining the mutual and self-inductance of the coils.

Referring now to FIGURES 8-10 of the drawings, another embodiment of thepresent invention is disclosed. The reactor of FIGURES 810 is exactlythe same electrically as that of FIGURES 1-7 and incorporates most ofthe features of the previously discussed reactor. However, the reactorof FIGURES 8-10 employs a plurality of insulating tie-rods 81, extendingfrom the radially extending arms of spider 23 to corresponding arms on 8spider 24. These rods are located interiorly of the innermost coils 25and serve the same purpose as insulating sleeve 21 in the previouslydescribed embodiment but have the added advantage of permittingincreased contact of a coolant gas or fluid with the most interiorreactor winding 25.

The rods 81 are threaded at each end and clamp the spiders 23 and 24together by compressional forces exerted by nuts 91 and 92,respectively, located at opposed ends of the tie-rods 81. A rubberWasher 93 is provided, if desired, between each nut and its respectivespider 23 or 24 for transmitting the compressional force exerted by nuts91, 92 to the spiders 23 and 24.

A longitudinal slot 94 is provided in each insulating tie-rod 81 topermit the arms of the respective spiders to be inserted therein. Theinterior coil element 25 may be wound directly onto the tie-rods 81 suchthat the latter supports the coil.

Spacers are provided between the adjacent coils in substantially thesame manner as for the previously described embodiment and suitablespacers retaining the coils in radial spaced relation are present.Likewise, insulating feet are located in the spider 24 and are radiallyadjustable for a particular mechanical spider configuration. The coilelement terminations are connected in substantially the same manner tospiders 23 and 24 as in the embodiment of FIGURES 1-7.

In manufacturing the reactors of both embodiments the coils aresuccessively wound one on another. In the embodiment of FIGURES 1-7, themost interior coil 25 is first completely Wound on sleeve 21 Withinsulating clamps 52 and 53 slightly removed from their final position.A plurality of insulating spacers 35 are then placed in contact with theexterior surface of coil 25 in a circumferential spaced relationship.The spacers 35 are initially secured to the body by glue or some otherbond which is not necessarily permanent. The second coil 26 is thenwound concentrically with coil 25 on spacers 35. A further group ofspacers are then placed on the exterior surface of coils 25. Thisoperation is continued until the desired number of coils has been wound.Clamps 52 and 53 are then tightened with the spacer and coilterminations respectively engaging claws 56 and 57. In the embodiment ofFIGURES 810, the same procedure is followed except that the first coil25 is wound on the rods 81. FIGURE 8 illustrates three coils 25, 26 and27 mound in concentric relationship.

The above described device may be used as a line wave trap wherein thepower transmission lines are used for communication purposes. In thisinstance, the entire assembly may be line carried and accordingly,weight is an important consideration. In this use the post insulators 71may be omitted. Furthermore, in this use, each coil may consist of twoconductors tightly wound onto one another to form a layer. Several suchlayers coaxially spaced may be used to form an air core reactor. Thespacing between the coils effectively provides an annular air ductextending axially the length of the coils. FIGURE 11 is a partialsectional elevational view illustrating a reactor 200 constructed inaccordance with the present invention. The reactor 200 consists ofconcentric coils 201 to 209 each comprising two side by side conductors210 and 211. Coils 201 to 203 are tightly wound one upon the other andform a layer 212 which is axially spaced from a layer 213 composed ofcoils 204 to 206 which is spaced from a layer 214 consisting of coils207, 208 and 209. A number of such layers may be used depending upon therequired rating of the trap. If desired the coils may be electricallyparalleled with a condenser to provide a tuned trap. The conductors areinsulated, e.g. varnished or the like insulaLed coating applied directlyon the electrically conductive wire.

The following is a further typical design of a device for use as a wavetrap or current limiting reactor constructed in accordance with thepresent invention:

Efieetive Mean Di- Current Winding Conductor Turns Winding ameter,Density, Conductor Length, inches Amps./ Weight, lbs.

inches in. 2

AXIAL COOLING DUCT A 1 2Wide6 A.W.G 68. 27 23.62 27.18 1,200 25.7 2 do66.13 22.88 27.48 1,200 25.2 3 d 64.26 22.23 27 79 1, 200 24,7

AXIAL COOLING DUCT AXIAL COOLING DUCT C 7 2Wide-4 A.W.G. 52. 85 22.7631.26 1,000 36.4 8 do 51.63 22.23 31.64 1,000 39.0 9 do 50.56 21.7732.02 1,000 35.7

AXIAL COOLING DUCT V AXIAL COOLING DUCT E 13 2wide-3 A.W.G 44.70 21.5035.82 1,000 44.5 14 do 44.14 21.22 36.24 1,000 44.5 15 do 43.65 21.0036.67 1,000 44.4

,6 AXIAL COOLING DUCT F 16 2wide-3 A.W.G 42.62 20.53 38.15 1,100 45.3 17do 42.56 20.46 38.58 1,100 45.6 18 do 42.55 20.45 39.00 1,100 46.1

AXIAL COOLING DUCT G 19 2Wide-3 A.W.Gr 42. 72 20.56 40.49 1,200 47.9 20do 42.89 20.62 40.91 1,200 48.8 21 .do 43.10 20.74 41.34 1,200 49.6

In the table on the foregoing pages, the letters A to G, respectively,each refers to the layer which consists of three windings. Layer A, forexample, is equivalent to layer 212. in FIGURE 11, which consists ofcoils 201, 202, and 203. Layer B would be equivalent to 213 in FIGURE11, while layer C would be equivalent to layer 214. The half-inchcooling duct referred to between each of the layers is an annular ductinterrupted about the periphery of the coil by the spacers. This coolingduct extends throughout the axial length of the coils.

The above wave trap wound from aluminum wire with double glazeinsulation has a rating of 1.5 millihenries and 1600 amps. The samedevice as a current limiting reactor has a rating of 60 cycles, .565 ohmreactance, 1600 amps voltage drop 904 volts 1447 kvar.

The mean diameters given in the table are realized by winding the wireof one winding into the groove between the wires of an adjacent winding.

While I have described and illustrated several specific embodiments ofmy invention, it will be clear that variations of the details ofconstructions which are specifically illustrated and described may beresorted to without departing from the true spirit and scope of theinvention as defined in the appended claims.

I claim:

1. An air core reactor comprising a plurality of separate, inductivelycoupled coils, concentrically disposed about a common axis, and selectedcoils being radially spaced from each other by a predetermined distance,said coils each having only one turn of conductor per axial pitch sothat each coil has only one layer of winding, said winding beinguntransposed by another coil, each coil winding being of a predeterminedlength with the respective coils terminating at peripherally spacedpoints about said common axis, and means for electrically connecting allof said coils in parallel said means making electrical contact with saidcoils at said peripherally spaced points.

2. An air core reactor adapted to be serially connected in a powertransmission line comprising a pair of spaced spiders includingelectrically conducting arms radiating therefrom, a plurality ofradially spaced layers of coaxial closely coupled coils disposed betweensaid spiders with each of said coils being electrically connectedselectively to said arms, each coil comprising an exact number of singleturn per axial pitch electrically insulated and untransposed windingseach of predetermined length and tightly wound one upon the other, saidarms electrically connecting said coils in parallel.

3. An air core reactor comprising a plurality of separate, inductivelycoupled insulated coils, each of said coils being concentric about acommon axis and radially spaced from each other by a predetermined,fixed distance, said coils being closely coupled and untransposed witheach of said coils having only one turn per axial pitch, the conductorcross sectional area of each coil, the axial pitch, number of turns anddiameter of each coil being such that the induced voltage across eachcoil is substantially equal for a preselected ratio of currents betweensaid coils, and a spider electrically connecting all of said coils inparallel said spider including electrically conducting arms extendingtherefrom with said coils selectively connected electrically to saidarms at various peripheral locations on said coils.

4. The reactor of claim 3 wherein the mutual and selfinductances of saidcoils as determined by the axial pitch, diameter and the number of turnsin each coil satisfied 5 the equations:

where p=number of coils in the reactor; r=1, 2, 3 p

s: l, 2, 3 p

(r and s may or may not be equal) n and n ==number of turns in coils rand 5, respectively;

M =specific mutual reactance between the rth and the sth coil, in whichspecific means the mutual reactance that would exist if each coilconsisted of only one effective turn, but is otherwise physicallyunchanged;

i current designed to flow through coils r, respectively;' andE=designed voltage drop across the reactor with the coil parametersselected so that the current distribution between the various coils iscompatible with the heat dissipation capabilities of the coils.

5. The reactor of claim 3 wherein the number of turns in each coil isdifferent hence necessitating termination of certain of said coils atdifferent peripherially spaced points about said axis.

6. The reactor of claim 5 wherein said electrically conducting arms ofsaid spider extend radially of said axis, one of said arms beingdisposed at each end of said coils and conductors extending parallel tothe axis of said coils and connecting the ends of said coils to saidarms.

7. A current limiting reactor comprising a plurality of separate,inductively coupled circular coils said coils being closely coupled anduntransposed, each of said coils being concentric about a common axis,and including only one turn per axial pitch, the cross sectional area ofeach coil being fixed and different than the cross sectional area ofothers of said coils, the conductor diameter of each coil, the axialwinding pitch, number of turns and diameter of each of said coils beingsuch that the induced voltage across each coil is substantially equalfor a preselected ratio of currents between said coils, and electricallyconducting spider means electrically connectinp all of said coils inparallel.

8. The reactor of claim 7 wherein certain of said coils terminate atdiiferent predetermined peripheral points about asid axis, and wherein apair of electrically conducting spiders are provided, each of saidspiders having arms extending from said axis, one of said spiders beingdisposed at each end of said coils, and electric conductors extendingparallel to said axis between each coil termination and the arms of thespider.

9. The reactor of claim 8 including an insulating sleeve havingventilating apertures, said sleeve being secured to the interior of thecoil having minimum radius, the arms of said spiders engaging oppositeends of said sleeve.

10. The reactor of claim 9 including a plurality of insulating spacersextending between said spider arms and interiorly of said coils, andmeans for securing said spider arms to said spacers.

11. The reactor of claim 1 wherein the mutual and self-inductances ofsaid coils as determined by the axial pitch, diameter and the number ofturns in each coil satisfies the equations:

where p=number of coils in the reactor; 1' 1, 2, 3 p s=1, 2, 3 p

References Cited by the Examiner UNITED STATES PATENTS 9/1915 Torchio336 5/1919 Brand 336-60 X LEWIS H. MYERS, Primary Examiner.

JOHN F. BURNS, ROBERT K. SCHAEFER,

Examiners. C. TORRES, Assistant Examiner.

1. AN AIR CORE STORAGE COMPRISING A PLURALITY OF SEPARATE, INDUCTIVELYCOUPLED COILS, CONCENTRICALLY DISPOSED ABOUT A COMMON AXIS, AND SELECTEDCOILS BEING RADIALLY SPACED FROM EACH OTHER BY A PREDETERMINED DISTANCE,SAID COILS EACH HAVING ONLY ONE TURN OF CONDUCTOR PER AXIAL PITCH SOTHAT EACH COIL HAS ONLY ONE LAYER OF WINDING, SAID WINDING BEINGUNTRASPOSED BY ANOTHER COIL EACH COIL WINDING BEING OF A PREDETERMINEDLENGTH WITH THE RESPECTIVE COILS TERMINATING AT PERIPHERALLY SPACEDPOINTS ABOUT SAID COMMON AXIS, AND MEANS FOR ELECTRICALLY CONNECTING ALLOF SAID COILS IN PARALLEL AND MEANS MARKING ELECTRICAL CONTACT WITH SAIDCOILS AT SAID PERIPHERALLY SPACED POINTS.